1. I always thought Sif should have spent some time as a Defender back in the day.

2. What is going on with Valkyrie these days exactly?

Well Fearless Defenders starts out with Val deciding which female Superheroes would make a Valkyrie to replace the old ones.
After a few events it's revealed she's the Valkyrie of Rage (each Valkyrie has a specialty power so to speak).
This new character without any powers and is an Archeologist, Annabelle, become one of the Defenders and..

Spoiler!!! Click to Read!:

Val see's what she mistakenly thinks is a Valkyrie spirit in Annabelle. Well long story short, Val has a berserker rage attack fights a bunch of heroines snaps out of it after killing Annabelle.
Annabelle ends up in Valhalla and doesn't want to be there, Val comes to her with Cela basically saying she didn't deserve to die and has Cela merge the two. which is where they left off in issue 7.